The present invention relates to a device for measuring the induction in the air gap of a magnetic bearing comprising a rotor armature made of ferromagnetic material, a stator constituted on the one hand by a frame made of ferromagnetic material defining a succession of poles and of notches in its part located opposite the rotor armature and, on the other hand, by electro-magnet coils disposed in the notches of said frame, and an air gap located between the rotor and the stator.
In an active magnetic bearing, the current for energizing the stator electro-magnets is controlled from the detection signals delivered by detectors which measure at every moment the displacements of the bearing rotor with respect to the stator, in order to maintain the rotor in a predetermined position.
The lifting force of a magnetic bearing is proportional to the square of the magnetic induction in the air gap of the bearing and to the useful active surface of the magnetic circuit of the bearing.
It is often useful to effect a precise measurement of the force of a bearing. This is the case, for example, when it is desired to measure the force of traction of a metal sheet resting on magnetic bearings.
In that case, the determination of the magnetic induction necessary for determining the lifting force is effected by a calculation which takes into account the result of different measurements, particularly of the air gap and the current for energizing the electro-magnets of the bearing. However, this method cannot take into account the remanent field of the electro-magnets. The error thus introduced remains relatively small, but becomes appreciable for certain applications.